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RISS 인기검색어
- 검색키워드
- 저자 : H. R. Jafarian (검색결과 3 건)
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Jafarian, H.R.,Anijdan, S.H. Mousavi,Eivani, A.R.,Park, N. Elsevier 2017 Materials science & engineering. properties, micro Vol.703 No.-
<P><B>Abstract</B></P> <P>The evolution of microstructure together with mechanical properties change of Fe-28.5Ni steel, used in design of marine and nuclear related products, processed by different deformation amount during ARB process was elaborated by Electron Backscattered Diffraction (EBSD) method. EBSD results showed that the initial structure of the material contained retained austenite as the main phase besides martensite phase. Martensite phase was diminished after successive ARB cycles due to reduction of martensite start (M<SUB>s</SUB>) temperature. EBSD microstructural results exhibited that a stabilized nano structure was attained by 6-cycle or 8-cycle of the ARB process with the latter having slightly higher grain size due to the grain growth effect of dynamic restoration mechanism resulting from extreme deformation. Tensile test data on different cycles of ARB processed specimens showed that yield and ultimate tensile strengths were substantially increased after the first cycle of the ARB coinciding with the substantial amount of dislocations in the form of low angle grain boundaries (LAGB). Strengths increased in the successive cycles, though in a much slower pace. Ultra-fine grains were formed instead after high cycles of ARB process. Although such increase in strength generally came at the expense of ductility, the material after 8-cycle had still substantial ductility.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fe-28.5Ni contained two phases of retained austenite and martensite. </LI> <LI> Martensite phase is reduced and austenite stabilized during ARB process. </LI> <LI> A nano grain size structure is developed after severe plastic deformation. </LI> <LI> Extreme deformation slightly increases the grain size by dynamic restoration process. </LI> <LI> Substantial amount of ductility was achieved in SPD due to austenite stabilization. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Nanostructural Evolution and Deformation Mechanisms of Severely Deformed Pure Fe
N. Forouzanmehr,H. R. Jafarian,M. Samadi‑khoshkhoo,M. Bönisch,M. Nili‑Ahmadabadi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6
Microstructural evolution and mechanical behavior of commercially pure Fe during severe deformation by cold caliber rollingfollowed by wire drawing were investigated using transmission electron microscopy and electron backscatter diffraction. Following by a drastic increment of strength in the early stage of deformation, shear banding as a softening mechanism leadsto decreasing of work hardening rate and finally a steady state situation at medium strains, creating a bimodal microstructure. Increasing strain beyond 3 is associated with increasing the rate of work hardening and refinement of the material. Severelydeformed Fe after cold caliber rolling to equivalent strain of 4.5 evolves from lamellar ultrafine-grained structure. Additionaldeformation by drawing results in more homogeneous structure and activates new mechanisms. A dynamic recovery appearsat severe strains through mechanically assisted triple junction motion. It is found that suppression of triple junction motionenhances the refinement of microstructure and the strength, such that the highly deformed Fe after equivalent strain of 7 hasa nano/ultrafine-grained structure combined with a high tensile strength of 1115 MPa.
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E. Naderi,A. Davoodi,H. R. Jafarian 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.11
Corrosion of WE43 magnesium alloys after equal-channel angular pressing (ECAP) process with one pass (1P), two pass(2P), three pass (3P) and four pass (4P) were investigated as a function of immersion time in 37 ± 2 °C simulated body fluid(SBF) to imitate body corrosion environment utilizing AC electrochemical impedance spectroscopy (EIS), Potentiodynamicpolarization (PDP) curves, SEM and optical microscopy techniques in addition to EDS analysis. Among the samples, 2P and3P samples illustrated better corrosion resistance not only among all the samples but also as a function of elapsed immersiontime in SBF media. Better corrosion resistance was related to precipitation of β particles with fair and large volume fractionwhich served as cathodic reaction sites. Uniform distribution of the reactions not only reduce the severity of micro-galvaniccorrosion but also by passing immersion time, anodic reaction dissolved magnesium substrate next to and around β phaseand separate them from the surface which resulted loss of cathodic sites and reduction of corrosion. Additionally, the morphologyof the β phase was changed from needle-like in 1P & 2P samples to spherical one in 3P & 4P samples. It is believeddiminished corrosion resistance of 4P samples not only among the ECAPed samples but also as a function of immersiontime, were related to coarsening of spherical β phase. In another word, corrosion reactions amplified and continued whileseparation of the phase from the surface was delayed due to its larger size.
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